The overall goal of this proposal is to understand the role played by activated mucosal T-cels and their cytokines in the immune mediated tissue damage seen in inflammatory bowel disease (IBD). Previous studies have shown an increased number of activated T-cells in the mucosa of IBD patients. Activation of mucosal T-cells by antibodies to the T-cell receptor in organ culture of normal fetal jejunum induces an enteropathy characterized by villus atrophy (epithelial damage) and crypt cell hyperplasia. This same change is seen near apthous ulcers in the mucosa of patients with Crohn's disease. Preliminary data is presented which demonstrate that activation of isolated mucosal T-cells, through the T- cell receptor (CD3) and the CD2 receptor, releases tumor necrosis factor- alpha (TNF-alpha) and gamma-interferon (IFN-gamma). Furthermore, the presence of both TNF-alpha as well as IFN-gamma in the supernatants was required to induce cytotoxicity of human colonic epithelial cells. These data duggest that cytokines produced and released by mucosal T-cells can be responsible for the epithelial damage that is obserfed in the two histopathological observations of mucosal injury described above. The studies in this proposal are based on the hypotheses that, in IBD, the inability to limit celllular injury to acute inflammation with healing (i.e., chronic epithelial damage) is a result of either 1) an encrease in release or different repertoires of T-cell associated cytokines; 2) defective ability to down regulate cytokine (TNF-alpha and/or IFN-gamma) production and/or release; or 3) enhanced receptor induction or post- receptor sensitivity of target epithelial cells to these cytokines. The in vitro system established will allow this initial study to focus on 1) understanding regulation of TNF-alpha and IFN-gamma transcription, induction and release from T-cell subsets in normal mucosa and compare these findings to the same T-cell subsets in IBD and 2) investigation of the mechanism of epithelial damage mediated by these cytokines. Specifically, these investigations will: 1. Define the phenotype(s) of mucosal T-cells that, upon activation, release TNF-alpha and/or IFN-gamma. 2. Define the regulation of TNF-alpha and IFN-gamma transcription, production and release from mucosal T-cells. 3. Determine the mechanism of TNF-alpha and IFN-gamma synergism of epithelial cell cytoxicity.